Hydraulic actuating system



Aug. 2, 1966 R. P. ROHDE HYDRAULIC ACTUATING SYSTEM Filed Sept. 25, 1963AT TORNEY United States Patent 3,263,425 HYDRAULHQ ACTUATING SYSTEMRobert P. Rohde, Saginaw, Mich, assignor to General Motors Corporation,Detroit, Mich, a corporation of Delaware Filed Sept. 23, 1963, Ser. No.310,560 4 Ulaims. (CI. 6052) This invention relates to hydraulicactuating systems wherein a hydraulic motor is fluid driven in either oftwo directions by a reversely drivable pump, and wherein one of themotor and pump has a greater difference in fluid displacement in onedirection of operation than does the other.

Since the volume of fluid delivered to the motor by the pump must equalthe fluid returned to the pump by the motor such directional differencein displacement presents a problem in handling the excess fluid returnedto the pump when driven in one direction, and in making up for thedeficiency of fluid returned thereto when the direction of operation isreversed. Although such difference in fluid displacement can becompensated for by employing a sump and a pump pressure operated shuttlevalve which will open the sump to alternate sides of the pump withchange in pump operating direction, these valves are subject to faultyoperation, and the large fluid displacement they require to insuresensitivity of their operation detracts from the sensitivity andeificiency sought in the actuation of the motor. Also, while it ispossible to mechanically link such a shuttle valve to the pump, such anarrangement has disadvantages in cost of construction and avoidance ofexcessive leakage if it is not to have an objectionable amount of lostmotion.

It is the object of my invention to compensate for the aforementioneddifference in fluid displacement by means which is relatively simple andinexpensive and which does not have any of the disadvantages of eitherthe pump pressure operated or the mechanically operated shuttle valve. Iobtain the desired result by arranging the sump with both an inlet andan outlet and providing valves controlling each so that fluid returnedfrom the motor in excess of fluid delivered thereto by the pump mayenter the sump, and fluid necessary to supplement that being returnedfrom the motor during operation in the opposite direction may be drawnfrom the sump. The valve controlling the sump inlet flow is mechanicallyresponsive to direction of pump operation, while the valve controllingsump outlet flow may be merely pressure responsive in operation.

The invention will be more clearly understood from the followingdescription of one preferred embodiment thereof which I have selectedfor purposes of illustration, having reference to the drawing, wherein:

FIGURE 1 is a longitudinal sectional view through a gear type pumphaving a sump associated therewith and showing a valve controlled inletto the sump in accordance with the invention.

FIGURE 2 is a transverse sectional view taken substantially along theline 22 of FIGURE 1, together with a hydraulic motor and associatedelements shown schematically arranged therewith and illustratingapplication of the invention to a hydraulic steering system of a motorvehicle.

FIGURE 3 is a fragmentary sectional view of the pump taken substantiallyalong the line 33 of FIGURE 1.

Referring now in detail to the drawing, and first to FIGURE 2, a geartype pump is shown designated generally by the numeral 1. Connected inclosed series fluid circuit with the pump, as represented by fluid lines2 and 3, are the respective ends 4 and 5 of a reversible hydraulic motor6. The motor is shown in the form of a power cylinder having a piston 7therein with a conmeeting rod 8 extending outwardly of the end 5 forreciprocal actuation of a vehicle steering system relay rod 9 whoseopposite ends are suitably hinged by links 19 and 11 to the vehicleframe 12 by means not shown. The end 4 of the power cylinder ispivotally anchored at 13 to this frame, and tie rods 14 and 15 pivotallylink the relay rod to steering arms 16 and 17 which dirigibly controlthe vehicle wheels 18 and 19.

The pump 1 comprises a housing 24 with meshing driving and driven gears25 and 26 which cooperate in conventional manner when rotated in thehousing chamber 27 to positively displace hydraulic fluid into eitherthe line 2 or the line 3, depending on the direction of rotation of thegears. It is to be understood, however, that the invention is notlimited to the use of this particular type pump, but may employ anyother known form of positive displacement pump which is reverselydrivable in accordance with the desired direction of actuation of themotor 5. Likewise, while the motor 5 illustrated is of the cylinder andpiston type, any other form of positive displacement motor may beemployed which is reversely drivable by the pump 1, it being onlynecessary in utilizing the principles of my invention that either themotor or the pump have a greater difference in fluid displacement thanthe other in one direction of operation than in the opposite direction.

A sump 28 is also provided, being shown in the form of an enclosureshell 29 surrounding the pump housing and secured and sealed thereto,respectively, as by the bolt 30 and gasket 30 seen in FIGURE 1. At theupper end of the shell 29 is an opening 31 through which hydraulic fluidsuch as oil may be introduced in filling the sump. Embracing theopposite ends of the pump housing 24 are housing end members 32 and 33,being held thereagainst by suitable studs 34 (FIGURE 2). The shafts 35and 36 of the respective pump gears are suitably journaled in bearings37 in each of these housing end members, and are suitably keyed as at 38and 39 to the pump gears. The oil level in the sump 38 will normally bemaintained above the level of the shaft 36, and this shaft is axiallydrilled to provide a lubricating passage 44 so that the hydraulic fluidin the sump is available at all times for lubrication of the bearings37, the oil entering this passage 40 through a connecting hole 41 in thehousing end member 32.

Means for driving the pump includes the shaft 35 which extends beyondits bearings 37 in the housing end member 33, and is suitably journaledin additional bearings 42 at its extended end. Journaled on these samebearings 42 within the housing end member 33 is a pump driving member 43which has a lost motion driving connection with the shaft 35. This lostmotion driving connection, as best seen in FIGURE 3, comprises radiallyopposite tongue portions 47 and 48 on the shaft 35 extending intorecesses 49 and 50 provided in the driving member 43. These recesses areof sufficient circumf-erential extent about the axis of the shaft 35that relative rotation between the shaft 35 and the member 43 may occur.The extent of this lost motion is adjustable by set screws 51 extendingoppositely toward the tongue 48 in the member 43 and a like set screw 51is disposed opposite one side of tongue 47. This tongue 47 is formedwith a pocket 52 for retaining a ball valve 53, and opposite the pocket52 is a ball seat 54 and a passage 54' extending therefrom through themember 43. Suflicient clearance is provided between the pocket 52 andthe ball seat 54 to accommodate fluid flow around the ball when thetongue 47 is in abutment with its set screw 51. Clearance 55 also isprovided within the member 43, inwardly of the recesses 49, 50, for theoil to circulate when the ball valve 53 is open, and a radial passage 56and a connecting axial passage 57 are provided in the 3 shaft 35 toconnect this clearance space 55 with a sump through an opening 58 inthe'housing end member 32.

FIGURE 1 shows a two-way thrust-bearing 6t) suitably secured in thehousing end member 33 to maintain the driving member 43 in properposition axially of the pump shaft 35, and spaced outwardly of thisthrust bearing is a suitable oil seal 61. Adjacent its inner end, theouter circumference of the driving member 43 is provided with an annulargroove 62, and on opposite sides of this groove are provided seals 63,64. An enlargement or boss 65, shown in FIGURE 3, is located on theexterior of the housing end member 33, and a passage 66 extendstherethrough to connect with this groove 62. A branch line 2' connectsline 2 with this passage 66. It will thus be seen that an inlet to thesump in the form of a one-way flow connection with the motor-pump line 2is provided via the branch line 2, boss passage 66, groove 62, passage54, clearance space 55, pump shaft passages 56 and 57 and housing endpassage 58.

An outlet from the sump is provided in the form of a one-way flowconnection with the opposite motor-pump line 3, as shown in FIGURE 2.This comprises a passage 67 extending through the pump housing 24 fromthe pump chamber 27 adjacent the connection to the latter by the fluidline 3. At its outer end, this passage communicates with a springchamber 68 within a projecting boss 69. At the outer end of this boss isa valve seat 76 against which a ball valve 71 is normally biased by acoil spring 72. A passage 73 in this valve seat, normally closed by theball valve 71, completes this second flow connection.-

During operation, by reason of the motor 6 having a greater fluiddisplacement during movement of its piston 7 toward the cylinder end 4than during movement of the piston toward the end 5, a greater volume offluid is returned by the motor to the line 2 than is delivered by thepump to line 3. Likewise, by reason of this same difference in fluiddisplacement of the motor, during movement of the piston 7 toward thecylinder end a smaller volume of fluid is returned by the motor to line3 than is delivered by the pump to line 2. In the former case (duringmovement of the piston to the right as shown in FIGURE 2) the pumpoperation is in the direction of the arrows shown in FIGURES 2 and 3,with the result that the pump driving member 43 tends to lead its drivenmember, i.e. shaft 35, and the ball valve 53 is thus enabled to uncoverthe passage 54. During such operation, the one-way flow connection ofbranch line 2, passages 66, 54, 56, 57 and 58 is open for returning tothe sump such excess fluid displaced by the motor. No loss of pump fluidpressure to the motor from the other side of the pump can occur, becausesuch pressure maintains the check valve 71 closed.

On the other hand, during movement of the motor piston to the left asviewed in FIGURE 2, the pump is operating in the opposite direction fromthat shown by the arrows in FIGURES 2 and 3, and the rotary lost motionbetween the pump driving member 43 and pump shaft 35 is taken up withthe result that the ball valve 53 is held tightly on its seat 54 so asto maintain the passage 54 closed. No loss of fluid pressure from line 2can thus occur via the branch line 2. The deficiency in fluid volumebeing returned via line 3 to the pump, relative to the pump fluid volumedelivered to the motor via line 2, tends to create a vacuum in thepassage 67 and spring chamber 68. As a result, the check valve 71 opens,admitting the necessary additional volume of fluid to that side of thepump from the sump 28.

It will thus be seen that my invention provides a very simple and lowcost arrangment for compensating for the difference in directional fluiddisplacement of the motor relative to that of the pump. The operation isautomatic yet requires no substantial amount of fluid displacement tooperate the one-way valves, and the valve members of both one-way flowconnections are self-sealing. It will be appreciated that various minorchanges in the construction and arrangement of the parts will readilysuggest themselves to persons skilled in the art Without departing fromthe spirit and scope of the invention as defined by the followingclaims.

I claim:

1. In combination with a reversely drivable hydraulic motor havinggreater fluid displacement in one direction of operation than in theopposite direction, a reversely drivable positive displacement pump influid driving relation with said motor, said pump having equal fluiddisplacement in both directions of operation, a sump having a firstone-way flow connection with the motor accommodating flow to the sump ofthe volume of motor displaced fluid exceeding the volume of pumpdelivered fluid during operation in said one direction and having asecond one-way flow connection with the pump accommodating flow of fluidto the pump to compensate for the volume of pump delivered fluidexceeding the volume of motor returned fluid during operation in saidopposite direction, and pump driving and driven members having a lostmotion connection therebetween, said first one-'way flow connectionincluding a passage in one of said members and a valve operable by theother of said members to close said passage when said lost motion istaken up in response to operation of the pump in said oppositedirection.

2. In combination with a reversely drivable hydraulic motor and areversely drivable hydraulic pump in closed circuit fluid drivingrelation with said motor, one of said motor and pump having asubstantially greater fluid displacement in one direction than in theopposite direction and the other of said motor and pump having moreequal fluid displacement in both directions of operation, a sump havingan inlet for fluid displaced from said one of said motor and pump inexcess of fluid returned thereto from the other thereof during operationin said one direction and on outlet for fluid to supplement the fluidreturned to said other thereof during operation in said oppositedirection, a valve controlling sump inlet fluid flow and a check valvecontrolling sump outlet fluid flow, and means for driving said pump,said inlet flow controlling valve being closable by said driving meansin response to operation of said pump in said opposite direction.

3. In combination with a reversible hydraulic motor having greater fluiddisplacement in one direction of operation than in the oppositedirection, a reversibly drivable positive displacement pump connected inclosed fluid circuit relation with said motor and having substantiallyequal fluid displacement in both directions of operation, a sump forreceiving fluid displaced by the motor in excess of fluid deliveredthereto by the pump during operation in said one direction and forsupplementing fluid return to the pump from the motor during operationin said opposite direction, pump driving means including driving anddriven members having limited lost motion therebetween, said drivingmember having a passage for said excess fluid flow to the sump, and avalve operable by said driven member to close said passage, said lostmotion accommodating opening said passage with operation of the pump insaid one direction.

4. In a hydraulic actuating system including a power cylinder closed ateach end, a piston operable therein and having a connecting rodextending outwardly of one end of the cylinder, a reversely drivablerotary pump connected in closed fluid circuit relation with therespective ends of the cylinder, a sump having an inlet and an outlet,said outlet being in fluid communication with said one end of thecylinder and having a check valve blocking flow into the sump via saidoutlet, driving means for the pump including a pump shaft and a memberhaving a rotary lost motion driving connection with said shaft, saidinlet comprising a passage in said member communicating at one end withthe sump and at its opposite end with the end of the cylinder remotefrom said con- 5 6 meeting rod, a valve seat on said member at said sumpReferences Cited by the Examiner communicating end of said passage, avalve engageable UNITED STATES PATENTS with said seat to close saidpassage and movable away from said seat to open said passage, said shafthaving a 2,640,322 6/1953 Puemer 60-52 portion engageable by said memberupon taking up said 5 2640426 6/1953 McLeod 60-52 X lost motion in onedirection and engageable with said 2,640,465 6/1953 60 52X valve to moveit against said seat upon taking up said lost 2:657-533 11/1953 Schanzlm60-52 motion in the opposite direction. EDGAR W. GEOGHEGAN, PrimaryExaminer.

1. IN COMBINATION WITH A REVERSELY DRIVABLE HYDRAULIC MOTOR HAVINGGREATER FLUID DISPLACEMENT IN ONE DIRECTION OF OPERATION THAN IN THEOPPOSITE DIRECTION, A REVERSELY DRIVABLE POSITIVE DISPLACEMENT PUMP INFLUID DRIVING RELATION WITH SAID MOTOR, SAID PUMP HAIVNG EQUAL FLUIDDISPLACEMENT IN BOTH DIRECTIONS OF OPERATION, A SUMP HAVING A FIRSTONE-WAY FLOW CONNECTIONS WITH THE MOTOR ACCOMMODATING FLOW TO THE SUMPOF THE VOLUME OF MOTOR DISPLACED FLUID EXCEEDING THE VOLUME OF PUMPDELIVERED FLUID DURING OPERATION IN SAID ONE DIRECTION AND HAVING ASECOND ONE-WAY FLOW CONNECTION WITH THE PUMP ACCOMMODATING FLOW OF FLUIDTO THE PUMP TO COMPENSATE FOR THE VOLUME OF PUMP DELIVERED FLUIDEXCEEDING THE VOLUME OF MOTOR RETURNED FLUID DURING OPERATION IN SAIDOPPOSITE DIRECTION, AND PUMP DRIVING AND DRIVEN MEMBERS HAVING A LOSTMOTION CONNECTION THEREBETWEEN, SAID FIRST ONE-WAY FLOW CONNECTIONINCLUDING A PASSAGE IN ONE OF SAID MEMBERS AND A VALVE OPERABLE BY THEOTHER OF SAID MEMBERS TO CLOSE SAID PASSAGE WHEN SAID LOST MOTION ISTAKEN UP IN RESPONSE TO OPERATION OF THE PUMP IN SAID OPPOSITEDIRECTION.